Conformal lining layers for damascene metallization

ABSTRACT

Method and structures are provided for conformal lining of dual damascene structures in integrated circuits. Trenches and contact vias are formed in insulating layers. The trenches and vias are exposed to alternating chemistries to form monolayers of a desired lining material. Exemplary process flows include alternately pulsed metal halide and ammonia gases injected into a constant carrier flow. Self-terminated metal layers are thus reacted with nitrogen. Near perfect step coverage allows minimal thickness for a diffusion barrier function, thereby maximizing the volume of a subsequent filling metal for any given trench and via dimensions.

REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.10/737,315 of Raaijmakers et al., filed Dec. 15, 2003, which is adivisional of U.S. patent application Ser. No. 09/644,416 of Raaijmakerset al., filed Aug. 23, 2000, which claims the priority benefit of U.S.provisional Application No. 60/159,799 of Raaijmakers et al., filed Oct.15, 1999 and provisional application No. 60/176,944 of Raaijmakers etal., filed Jan. 18, 2000.

FIELD OF THE INVENTION

The invention relates generally to forming lining layers in highaspect-ratio voids during the fabrication of integrated circuits, andmore particularly to barrier layers lining trenches and contact vias indual damascene metallization schemes.

BACKGROUND OF THE INVENTION

When fabricating integrated circuits, layers of insulating, conductingand semiconducting materials are deposited and patterned to producedesired structures. “Back end” or metallization processes includecontact formation and metal line or wire formation. Contact formationvertically connects conductive layers through an insulating layer.Conventionally, contact vias or openings are formed in the insulatinglayer, which typically comprises a form of oxide such asborophosphosilicate glass (BPSG) or oxides formed fromtetraethylorthosilicate (TEOS) precursors. The vias are then filled withconductive material, thereby interconnecting electrical devices andwiring above and below the insulating layers. The layers interconnectedby vertical contacts typically include horizontal metal lines runningacross the integrated circuit. Such lines are conventionally formed bydepositing a metal layer over the insulating layer, masking the metallayer in a desired wiring pattern, and etching away metal between thedesired wires or conductive lines.

Damascene processing involves forming trenches in the pattern of thedesired lines, filling the trenches with a metal or other conductivematerial, and then etching the metal back to the insulating layer. Wiresare thus left within the trenches, isolated from one another in thedesired pattern. The etch back process thus avoids more difficultphotolithographic mask and etching processes of conventional metal linedefinition.

In an extension of damascene processing, a process known as dualdamascene involves forming two insulating layers, typically separated byan etch stop material, and forming trenches in the upper insulatinglayer, as described above for damascene processing. After the trencheshave been etched, a further mask is employed to etch contact viasdownwardly through the floor of the trenches and the lower insulatinglayer to expose lower conductive elements where contacts are desired.

Conductive elements, such as gate electrodes, capacitors, contacts,runners and wiring layers, must each be electrically isolated from oneanother for proper integrated circuit operation. In addition toproviding insulating layers around such conductive elements, care mustbe taken to prevent diffusion and spiking of conductive materialsthrough the insulating layers, which can cause undesired short circuitsbetween among devices and lines. Protective barriers are often formedbetween via or trench walls and metals in a substrate assembly, to aidin confining deposited material within the via or trench walls. Barriersare thus useful for damascene and dual damascene interconnectapplications, particularly for small, fast-diffusing elements such ascopper.

Candidate materials for protective barriers should foremost exhibiteffective diffusion barrier properties. Additionally, the materialsshould demonstrate good adhesion with adjacent materials (e.g., oxidevia walls, adhesion layers, etch stop layers and/or metallic materialsthat fill the vias and trenches). For many applications, a barrier layeris positioned in a current flow path and so must be conductive.Typically, barriers have been formed of metal nitrides (MN_(x)), such astitanium nitride (TiN), tantalum nitride (TaN), and tungsten nitride(WN), which are dense and adequately conductive for lining contact vias,wiring trenches, and other conductive barrier applications.

These lined vias or trenches are then filled with metal by any of avariety of processes, including chemical vapor deposition (CVD),physical vapor deposition (PVD), and electroplating. For effectiveconductivity and to avoid electromigration during operation, the metalof a contact or wiring layer should fill the via or trench withoutleaving voids or key holes. Completely filling deep, narrow openingswith conductive material is becoming ever more challenging as integratedcircuit dimensions are constantly scaled down in pursuit of fasteroperational processing speeds and lower power consumption.

As illustrated in FIGS. 1 to 2, utilizing a conductive barrier layerand/or other liners makes filling the trenches and vias of dualdamascene processing even more difficult. FIG. 1 illustrates a dualdamascene process in which an upper insulating layer 10 is formed over alower insulating layer 12, which is in turn formed over a conductivewiring layer 14, preferably with an intervening dielectric diffusionbarrier 15. This dielectric barrier 15 serves to prevent copper or otherconductive material of the underlying runner 14 from diffusing into theoverlying dielectric layer 12.

A mask is employed to pattern and etch trenches 16 in a desired wiringpattern. In the illustrated embodiment, the trench 16 is etched down tothe level of an etch stop layer 19, which is formed between the twoinsulating layers 10, 12. This etch stop layer 19 is typically patternedand etched, prior to deposition of the upper insulating layer 10, toform a hard mask that defines horizontal dimensions of desired contactvias that are to extend from the bottom of the trench 16. Continuedetching through the hard mask 19 opens a contact via 20 from the bottomof the trench 16 to the lower conductive wiring layer 14. FIG. 1 alsoshows an upper etch stop or chemical mechanical polishing (CMP) stoplayer 21 over the upper insulating layer 10 to stop a laterplanarization step, as will be appreciated by the skilled artisan.

Protective liners 22, preferably formed of conductive material, are thenformed on the exposed horizontal and sidewall surfaces. Typically, theliners 22 at least include a metal nitride, and may additionally includeadhesion enhancing and seeding layers. For example, the liner 22 cancomprise a tri-layer of Ti/TiN/Cu. In such a structure, the titaniumlayer serves to improve adhesion with exposed oxide sidewalls; thetitanium nitride serves as a diffusion barrier; and a thin copper layerserves as a seed for later electroplating of copper. In other examples,the liners 22 can include tantalum nitride or tungsten nitride barriers.

Conformal deposition of the liners 22, however, is very difficult withconventional processing. For example, physical vapor deposition (PVD),such as sputtering, of a metal layer (for adhesion, barrier and/or seedlayer) requires at least about 50 Å over all surfaces of the trench 16and contact via 20. Unfortunately, PVD of metal into high aspect ratiovoids necessitates much greater deposition on the top surfaces of theworkpiece to produce adequate coverage of the via bottom. For example,typical state-of-the-art trench and contact structures for dualdamascene schemes require about 500 Å PVD metal in order for 50 Å ofmetal to reach the bottom and sidewalls of the contact 20.

This poor step coverage is a result of the high aspect ratio of voidsformed for dual damascene processing in today's integrated circuitdesigns. The aspect ratio of a contact via is defined as the ratio ofdepth or height to width. In the case of dual damascene contacts, thetrench 16 and contact via 20 together reach through two levels ofinsulating layers 10, 12, such that the effective aspect ratio of thevia 20 is very high.

Conventional deposition processes produce very poor step coverage (i.e.,the ratio of sidewall coverage to field or horizontal surface coverage)of such high aspect ratio vias for a variety of reasons. Due to thedirectionality of PVD techniques, for example, deposition tends toaccumulate more rapidly at upper corners 26 of the trench 16 and uppercorners 28 of the via 20, as compared to the via bottom 30. As a resultof the rapid build-up of deposited material the upper surfaces of thestructure, the liners occupy much of the conductive line width in thetrench 16 and even more, proportionately, of the contact via 20. Thesebuilt-up corners 26, 28 then cast a shadow into the lower reaches of thestructure, such that lower surfaces, and particularly lower corners, aresheltered from further deposition. Although PVD deposition can bedirected more specifically to the via bottom, e.g., by collimation or byionization of the depositing vapor, such additional directionality tendsto sacrifice sidewall coverage.

Chemical vapor deposition (CVD) processes have been developed forcertain metals and metal nitrides. CVD tends to exhibit better stepcoverage than PVD processes. In order for CVD processes to exhibit goodstep coverage, the reaction must be operated in the so-called “surfacecontrolled” regime. In this regime, reaction species do not adhere totrench or via walls upon initial impingement. Rather, the species bounceoff trench/via surfaces several times (e.g., 10-500 times) beforereacting.

State-of-the-art CVD processes for depositing barrier layers attemperatures sufficiently low to be compatible with surroundingmaterials do not operate completely within the surface-controlledregime. Accordingly, even CVD processes, tend to deposit far lessmaterial at the bottom of a dual damascene contact 20 then on the uppersurfaces and sidewalls of the structure. The upper corners of the trench16 and the contact 20 represent a high concentration of surface area tovolume. Deposition upon the horizontal upper surfaces and adjacentvertical sidewall surfaces merge together to result in an increaseddeposition rate near the corners 26, 28. Additionally, flowing reactantsdiffuse slowly into the confined spaces of the trench 16 and contact 20.Accordingly, the concentration of reactants reaching the via bottom 30is far reduced relative to the concentration of reactants reaching uppersurfaces of the structure. Thus, while somewhat improved relative toPVD, CVD step coverage of dual damascene structures remains uneven withmost currently known low temperature CVD techniques.

In the pursuit of faster operational speeds and lower power consumption,dimensions within integrated circuits are constantly being scaled down.With continued scaling, the aspect ratio of contacts and trenchescontinues to increase. This is due to the fact that, while the width orhorizontal dimensions of structures in integrated circuits continues toshrink, the thickness of insulating layers separating metal layerscannot be commensurately reduced. Reduction of the thickness in theinsulating layers is limited by the phenomenon of parasitic capacitance,whereby charged carriers are slowed down or tied up by capacitanceacross dielectric layers sandwiched by conductive wires. As is known,such parasitic capacitance would become disabling if the insulatinglayer were made proportionately thinner as horizontal dimensions arescaled down.

With reference to FIG. 2, a scaled-down version of FIG. 1 is depicted,wherein like parts are referenced by like numerals with the addition ofthe suffix “a.” As shown, continued scaling leads to a more pronouncedeffect of uneven step coverage while lining dual damascene structures.Material build-up at the corners 28 a of the contact via 20 a quicklyreduces the size of the opening, even further reducing the concentrationof reactants that reach into the contact via 20 a. Accordingly, coverageof the via bottom surface 30 a drops off even faster. Moreover, thepercentage of the trench 16 a occupied by the liner materials is muchgreater for the scaled down structure of FIG. 2. Since the liningmaterial is typically less conductive than the subsequent filler metal(e.g., copper), overall conductivity is reduced. Worse yet, cusps at thecorners 28 a of the contact via can pinch off before the bottom 30 a issufficiently covered, or during deposition of the filler metal.

Accordingly, a need exists for more effective methods of lining trenchesand vias in integrated circuits, particularly in the context of dualdamascene metallization.

SUMMARY OF THE INVENTION

In satisfaction of this need, methods are provided herein for depositinglining materials into the high-aspect ratio trenches and contact vias ofdual damascene metallization schemes. Advantageously, the methods attainhigh step coverage, such that only the minimum required thickness of thelining layer need be formed on all surfaces. Examples are provided forapplying the methods to formation of one or more of adhesion, barrierand electroplating seed layers.

In general, the methods comprise cycles of alternating reactant phases,wherein each phase has a self-limiting effect. “Pure” metal layers, forexample, can be formed by alternately adsorbing self-saturating halide-or organic-terminated metal monolayers and reducing the metal-containingmonolayer. Metal nitrides suitable for conductive diffusion barriers canbe formed by alternately adsorbing self-terminated metal-containingmonolayers and conducting ligand exchange reactions, substitutingnitrogen-containing species for halogen or organic tails on themetal-containing monolayers. Alternatively, the tails of theself-terminated metal-containing monolayer can be reduced or otherwiseremoved in an intermediate scavenger or getter phase prior to thenitrogen phase.

Advantageously, the methods enable forming uniformly thick conductivelayers within high-aspect ratio openings (e.g., trenches and vias),desirably as thin as possible consistent with their respectivefunctions. The remaining volume within such openings is thus maximized,facilitating a greater proportionate volume of more highly conductivefiller materials, such as copper for metal runners and integralcontacts.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the invention will be readily apparent to theskilled artisan in view of the description below, the appended claims,and from the drawings, which are intended to illustrate and not to limitthe invention, and wherein:

FIG. 1 is a schematic cross-section of a dual damascene structure havinga conventional barrier layer lining the trench and contact via thereof;

FIG. 2 generally illustrates a lined dual damascene structure, similarto FIG. 1, for a scaled-down integrated circuit;

FIG. 3 is a flow chart generally illustrating a method of lining highaspect ratio, dual damascene structures prior to filling with a morehighly conductive material;

FIG. 4 is an exemplary gas flow diagram for depositing a barrier layer,in accordance with a preferred embodiment of the present invention; and

FIG. 5-13 are schematic cross-sections of a partially fabricatedintegrated circuit, generally illustrating the construction, lining andfilling of a trench and via formed in insulating layers above asemiconductor substrate, in accordance with a preferred dual damasceneprocess flow.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Though described in the context of certain preferred materials, it willbe understood, in view of the disclosure herein, that the methods andstructures described herein will have application to a variety of othermaterials for lining damascene structures.

As discussed in the Background section above, lining damascenestructures, and particularly dual damascene structures, by physicalvapor deposition (PVD) and conventional chemical vapor deposition (CVD)disadvantageously fills a large volume of the trenches and contact vias.Accordingly, less room is left for the highly conductive filler materialto follow. Use of a thinner liner material would leave more room forhighly conductive filler metals such as copper which would, in turn,increase conductivity and operational signal transmission speeds for theintegrated circuit. Conventional methods such as PVD and CVD, by theirvery nature, produce thicker layers towards the upper end of thedamascene structure than at the bottom. While much research has beendevoted to obtaining more conformal step coverage of dual damascenetrenches and contact vias, it is very difficult to supply the sameconcentration of reactant species (or PVD sputtered material) to allsurfaces of such structures. In particular, it is difficult to supplythe same concentration of depositing species at the upper surfaces ofsuch structures as supplied to the bottom of deep, confined contact viasthat extend from the bottom of an already-deep trench.

By providing almost perfect step coverage, the preferred embodimentsadvantageously obtain the minimum necessary thickness for the desiredliner layers over all surfaces of trenches and contact vias in a dualdamascene structure. Desirably, the methods of the preferred embodimentare less dependent upon the relative concentration of reactant speciesin upper regions as compared to lower regions of the trench and contactvia.

With reference to FIGS. 5-8, insulating layers are formed over asemiconductor substrate, in accordance with the preferred embodiments.Referring initially to FIG. 5, first or lower insulating layer 50 isformed over a barrier layer 51 and a conductive element 52, which formspart of a lower interconnect layer in the illustrated embodiment. Aswill be appreciated by the skilled artisan, metallization schemestypically employ one metal composition throughout various wiring layers(e.g., copper interconnects or aluminum interconnects). The preferredembodiments are adaptable to many different materials, but certainembodiments are particularly adapted to lining damascene structureswherein the via floor or lower conductive element 52 comprises a highlyconductive copper line. The first insulating layer 50 is preferablyformed to a thickness sufficient to insulate the lower conductiveelement 52 from upper wiring structures to be formed. An etch stop layeror hard mask 54 (FIGS. 6-7) is formed over the lower insulating layer 50and a second or upper insulating layer 56 (FIG. 8) is formed over theetch stop layer 54. A second etch or CMP stop layer 58 (also known as ashield layer) is preferably also formed over the upper insulating layer56.

In the illustrated embodiment, each of the lower and upper insulatinglayers 50, 56 comprise oxide deposited by plasma enhanced CVD employingtetraethlyorthosilicate a precursor. The insulating layers 50, 56 of thepreferred material (referred to in the industry as “PECVD TEOS”) arepreferably provided with a thickness between about 0.3 μm and 1.5 μm,more preferably between about 0.5 μm and 1.0 μm. The skilled artisanwill readily appreciate that the insulating layer can comprise any of anumber of other suitable dielectric materials. For example, dielectricmaterials have recently been developed that exhibit low permittivity(low k), as compared to conventional oxides. These low k dielectricmaterials include polymeric materials, porous materials andfluorine-doped oxides. The present methods of lining trenches andcontact vias will also have utility in conjunction with such low kmaterials.

The etch stop layers 54, 58 of the illustrated embodiment each comprisea material exhibiting different etch rates relative to the insulatinglayers 50, 56, allowing better control of etching processes. In theillustrated embodiment, the etch stop layers 54, 58 comprise siliconnitride (Si₃N₄), preferably provided to a thickness of between about 100Å and 700 Å, and more preferably between about 200 Å and 500 Å. Thelower barrier layer 51 preferably also comprises Si₃N₄.

As discussed in the Background section above, after the lower insulatinglayer 50 and etch stop 54 are formed (FIGS. 5 and 6), a mask and etchprocess transfers a pattern of openings 55 (one shown in FIG. 7) to theetch stop 54. The second or upper insulating layer 56 and optional CMPstop 58 are then formed over the hard mask 54.

With reference now to FIG. 9A, the substrate is masked and trenches 60(one shown) are etched through the upper insulating 56, preferablystopping on exposed portions of the first etch stop layer 54. As will beunderstood by the skilled artisan, the trenches 60 are etched across theinsulating layer 56 in patterns desired for metal lines, in accordancewith an integrated circuit design: In the illustrated embodiment, thewidth of the trench is less than about 0.35 μm and more preferably lessthan about 0.25 μm.

Continued etching through the hard mask 54 defines contact vias 62 (oneshown) extending downwardly from the bottom of the trench and throughthe lower insulating layer 50 to expose conductive elements below (e.g.,metal line 52). The contact vias 62 are defined by the openings 55 inthe hard mask 54 at discrete locations along the trenches 60. Desirably,the contact vias 62 have a width of less than about 0.35 μm and morepreferably between about 0.05 μm and 0.25 μm. The width or the diameterof a contact via 62 can be equal to or slightly less than the line widthdefined by the trench 60 above.

The effective aspect ratio (depth:width) of the contact via 62 istherefore preferably greater than about 2:1. Since the effective depthof the contact via 62 is defined through both insulating layers 50, 56,the effective aspect ratio is more preferably greater than about 3:1,and most preferably between about 4:1 and 8:1. The preferred embodimentswill have particular utility in connection with future generationdevices, whereby line widths and contact widths will shrink evenfurther.

With reference to FIGS. 9B to 9D, the preferred embodiments also haveparticular utility in conjunction with variations on the dual damascenestructure of FIG. 9A. Parts similar to those of FIG. 9A will be referredto by like reference numerals.

Referring to FIG. 9B, a non-capped dual damascene structure is shown.When non-capped vias 62 are allowed by design rules (and they aredesirable for obtaining higher circuit densities), mask misalignment canlead to even greater aspect ratios. As one via sidewall is withdrawnfrom the corresponding edge of the opening 55 defined by the hard mask54, the effective contact size decreases, such that aspect ratios caneasily be double those listed above for the illustrated embodiment ofFIG. 9A.

Referring now to FIG. 9C, vias that are not fully landed similarlyexhibit higher effective aspect ratios. Under such circumstances, theopening 55 of the hard mask 54 overlaps with an edge 70 of theconductive circuit element 52. Small but very high aspect ratio overetchholes 72 are formed in an insulating or dielectric layer 74 surroundingthe circuit element 52. The depth of the overetched hole 72 will depend,of course, on the etch selectivity between the barrier layer 51 and thesurrounding dielectric 74.

FIG. 9D illustrates the effect of undercutting the barrier layer 51during via etch. When the barrier 51 is etched by a selective etch fromthe via bottom to expose the underlying circuit element 52, the barrier51 tends to be laterally recessed. The resultant cavities 80 are verydifficult to line by conventional processes.

FIG. 9E illustrates yet another non-ideal damascene structure. Whenremoving photoresist employed to pattern the structure, insulatinglayers 50, 56 formed of low k dielectrics are susceptible to attack,leaving a barrel-shaped profile in the trench 60 and via 61. Thisstructure is also difficult to effectively line and fill by conventionalprocessing.

Similarly, many other non-ideal conditions can result in otherre-entrant profiles, cavities and/or extremely high aspect ratios fordual damascene trenches and vias. Under such circumstances, conventionalprocessing is inadequate for lining and filling these structures withoutforming voids. The methods of the preferred embodiments, in contrast,can effectively line even the aberrant structures of FIGS. 9B to 9E.Moreover, the skilled artisan will readily find application for themethods and films disclosed herein beyond the dual damascene context.For example, the methods disclosed herein can also be used effectivelyfor lining trenches in single damascene wiring schemes or for liningconventional contact vias and openings. The methods of lining haveparticular utility in conjunction with the dual damascene process flowsof the preferred embodiments.

Methods of Forming Conformal Liners

The damascene structure so formed is thereafter lined with high stepcoverage. In accordance with the preferred embodiments, liners areformed by a periodic process in which each cycle deposits, reacts oradsorbs a layer upon the workpiece in a self-limiting manner.Preferably, each cycle comprises at least two distinct phases, whereineach phase is a saturative reaction with a self-limiting effect, leavingno more than about one atomic monolayer of the desired liner material.

FIG. 3 generally illustrates a method of forming damascene lining layerswith high step coverage. The preferred method is a form of atomic layerdeposition (ALD), whereby reactants are supplied to the workpiece inalternating pulses in a cycle. Preferably, each cycle forms no more thanabout one monolayer of lining material by adsorption and preferably bychemisorption. The substrate temperature is kept within a windowfacilitating chemisorption. In particular, the substrate temperature ismaintained at a temperature low enough to maintain intact bonds betweenadsorbed species and the underlying surface, and to preventdecomposition of the reactant species. On the other hand, the substratetemperature is maintained at a high enough level to avoid condensationof reactants and to provide the activation energy for the desiredsurface reactions in each phase. Of course, the appropriate temperaturewindow for any given ALD reaction will depend upon the surfacetermination and reactant species involved.

Each pulse or phase of each cycle is preferably self-limiting in effect.In the examples set forth below, each of the phases are self-terminating(i.e., an adsorbed and preferably chemisorbed monolayer is left with asurface non-reactive with the chemistry of that phase). An excess ofreactant precursors is supplied in each phase to saturate the structuresurfaces. Surface saturation ensures reactant occupation of allavailable reactive sites (subject to physical size restraints, asdiscussed in more detail below), while self-termination prevents excessfilm growth at locations subject to longer exposure to the reactants.Together, saturation and self-terminating chemistries ensure excellentstep coverage.

As illustrated, the process in accordance with the preferred embodimentsbegins with formation 100 of a dual damascene structure, such as thoseillustrated in FIGS. 9A to 9D and discussed above.

If necessary, the exposed surfaces of the dual damascene structure(e.g., the trench and via sidewall surfaces and the metal floor shown inFIG. 9A, or surfaces of a previously deposited adhesion layer) areterminated 102 to react with the first phase of the ALD process. Thefirst phases of the preferred embodiments (see Tables I to IV) arereactive, for example, with hydroxyl (OH) or ammonia (NH₃) termination.In the examples discussed below, silicon oxide and silicon nitridesurfaces of the dual damascene structure do not require a separatetermination. Certain metal surfaces, such as at the bottom of the via 61(FIG. 9A), can be terminated, for example, with ammonia treatment. Wherethe lining material to be deposited is a metal nitride, surfacetermination can be considered to include formation of an initialadhesion layer and surface termination thereof, as discussed in moredetail with respect to Table I below, possibly with an additionalsurface termination treatment of the adhesion layer.

After initial surface termination 102, if necessary, a first chemistryis then supplied 104 to the workpiece. In accordance with the preferredembodiments, discussed in more detail below with respect to FIG. 4, thefirst chemistry comprises a metal-containing compound that is reactivewith the terminated surfaces left by the previous step 102. Accordingly,a metal-containing species replaces or adsorbs upon the surfacetermination. This metal-containing species layer is desirablyself-terminating, such that any excess constituents of the firstchemistry do not further react with the monolayer formed by thisprocess. Preferably a halide or organic ligand terminates themetal-containing monolayer.

The metal-containing reactive species is preferably supplied in gaseousform, and is accordingly referred to hereinbelow as a metal gas source.In some examples, the reactive species actually has a melting pointabove the process temperature (e.g., in Table V below, CuCl melts at430° C. while the process is conducted at about 350° C.). Nevertheless,the metal source gas is considered “volatile,” for purposes of thepresent description, if the species exhibits sufficient vapor pressureunder the process conditions to transport the species to the workpiecein sufficient concentration to saturate exposed surfaces.

The first chemistry is then removed 106 from the reaction chamber. Inthe illustrated embodiments, step 106 merely entails stopping the flowof the first chemistry while continuing to flow a carrier gas for asufficient time to diffuse or purge excess reactants and reactantby-products out of the vias, trenches and the reaction chamber,preferably with greater than about two reaction chamber volumes of thepurge gas, more preferably with greater than about three chambervolumes. In the illustrated embodiment, the removal 106 comprisescontinuing to flow purge gas for between about 0.1 seconds and 20seconds after stopping the flow of the first chemistry. Inter-pulsepurging is described in co-pending U.S. patent application having Ser.No. 09/392,371, filed Sep. 8, 1999 and entitled IMPROVED APPARATUS ANDMETHOD FOR GROWTH OF A THIN FILM, the disclosure of which isincorporated herein by reference. In other arrangements, the chamber maybe completely evacuated between alternating chemistries. See, forexample, PCT publication number WO 96/17107, published Jun. 6, 1996,entitled METHOD AND APPARATUS FOR GROWING THIN FILMS, the disclosure ofwhich is incorporated herein by reference. Together, the adsorption 104and reactant removal 106 represent a first phase in an ALD cycle.

When the reactants of the first chemistry have been removed 106 from thechamber, a second chemistry is supplied 108 to the workpiece. The secondchemistry desirably reacts with the self-terminated monolayer formed instep 104. In the illustrated embodiments, described in more detail belowwith respect to FIG. 4, this reaction comprises supplying a nitrogensource gas to the workpiece. Nitrogen or nitrogen-containing speciesfrom the nitrogen source gas preferably reacts with the previouslyadsorbed metal-containing species to leave a metal nitride in place ofthe metal-containing monolayer.

In other arrangements, the second chemistry may simply scavenge orremove the ligand termination of the adsorbed metal complex monolayerformed in step 104 (e.g., by ligand-exchange, sublimation or reduction)or otherwise prepare the monolayer for deposition/adsorption of afurther monolayer and/or reaction with a further chemistry (see, e.g.,Tables I, IV and V below). Desirably, the reaction 108 is alsoself-limiting. Reactants saturate the limited number of reaction sitesleft by step 104. Temperature and pressure conditions are preferablyarranged to avoid diffusion of reactants from the second chemistrythrough the monolayer to underlying materials. The second chemistry alsoleaves a surface termination that operates to limit the deposition in asaturative reaction phase. In the illustrated embodiments of Tables IIand III below, nitrogen and NH_(x) tails terminating a metal nitridemonolayer are non-reactive with NH₃ of the second chemistry.

After a time period sufficient to completely saturate and react themetal-containing monolayer with the second chemistry, the secondchemistry is removed 110 from the workpiece. As with the removal 106 ofthe first chemistry, this step 110 preferably comprises stopping theflow of the second chemistry and continuing to flow carrier gas for atime period sufficient for excess reactants and reaction by-productsfrom the second chemistry to diffuse out of the vias and trenches of thedamascene structure and be purged from the reaction chamber. Forexample, reactants and reaction by-products can be removed by flowingpurge gas after stopping the flow of the first chemistry, preferablywith at least about two chamber volumes of purge gas and more preferablywith at least about three chamber volumes. In the illustratedembodiment, the removal 110 comprises continuing to flow purge gas forbetween about 0.1 seconds and 20 seconds after stopping the flow of thefirst chemistry. Together, the reaction 108 and removal 110 represent asecond phase 111 in an ALD cycle.

In the illustrated embodiment, where two phases are alternated once theexcess reactants and by-products of the second chemistry have diffusedout of the vias and trenches, and preferably out of the reactionchamber, the first phase of the ALD process is repeated. Accordingly,again supplying 104 the first chemistry to the workpiece forms anotherself-terminating monolayer.

The two phases 107, 111 thus represent a cycle 115 repeated to formmonolayers in an ALD process. The first chemistry generally reacts withthe termination left by the second chemistry in the previous cycle. Ifnecessary, the cycle 115 can be extended to include a distinct surfacepreparation, similar to step 102, as shown in dotted lines in FIG. 3.The cycle 115 then continues through steps 104 to 110. This cycle 115 isrepeated a sufficient number of times to produce a lining layer withinthe dual damascene structure of a thickness sufficient to perform itsdesired function.

Though illustrated in FIG. 3 with only first and second chemistries, itwill be understood, that, in other arrangements, additional chemistriescan also be included in each cycle (see, e.g., Table IV below).Furthermore, though illustrated with an initial metal phase andsubsequent nitrogen phase in the examples below, it will be understoodthat the cycle can begin with the nitrogen phase, depending upon thesurfaces and phase chemistries.

Forming Metal Adhesion Liners

Depending upon the exposed materials and desired ALD chemistry, anadhesion layer prior to formation of a barrier diffusion may or may notbe desired. With TEOS oxides, the inventors have not found the use of anadhesion layer necessary. On the other hand, adhesion layers may bedesirable for vias and trenches formed in alternative insulatingmaterials, such as spin-on dielectrics and low k materials. Conductiveadhesion layers may also be desirable to facilitate reaction of thefirst phase over metal runners or landing pads 52 exposed at the bottomof the via 61 (FIG. 9A).

If an adhesion layer is desired, the adhesion layer preferably comprisesa “pure” metal lining layer over oxide, metal and etch stop layers ofthe dual damascene structures. Prior to forming the preferred barrierlayers, therefore, a dual damascene structure similar to those of FIGS.9A to 9E is preferably lined with a metal adhesion layer. As is known inthe art, such adhesion layers can be formed by PVD or CVD. For example,PVD titanium and CVD tungsten processes are well known in the art.

More preferably, the adhesion layer is formed by ALD, as exemplified bythe process recipe of Table I below. It will be understood that theprinciples disclosed herein with respect to FIG. 3, and with respect tothe particular examples of metal nitrides set forth below, areapplicable to the formation of a variety liner materials. For example, apure metal layer can be deposited by alternately depositing halogen- ororganic-terminated monolayers of metal and flowing reduction agents(e.g., H radicals, triethyl boron or other strong reducers) to removethe halogen termination. Removal of the metal monolayer termination bybinding and carrying the ligand away can be more generally referred toas “gettering” or “scavenging” the ligand. In the next cycle, therefore,the metal source gas can adsorb upon the underlying metal monolayer inanother self-terminating phase. The resultant ALD metal is particularlyuseful as an adhesion layer prior to barrier layer deposition, and as aseed layer following barrier deposition and preceding electroplating.

Accordingly, one of the reactant species preferably includes ametal-containing species with an organic or halide ligand. Exemplarymetal precursors include tantalum pentaethoxide,tetrakis(dimethylamino)titanium, pentakis(dimethylamino)tantalum, TaCl₅and TiCl₄. In the illustrated embodiment, a tungsten (W) seed layer isformed by ALD, in alternating metal and reducing phases separated bypurge steps. In the process recipe of Table I below, tungstenhexafluoride (WF₆) is alternated with a scavenger in the form of thereducing agent triethyl boron ((CH₃CH₂)₃B) or TEB. TABLE I CarrierReactant Flow Flow Temperature Pressure Time Phase (slm) Reactant (sccm)(° C.) (Torr) (sec) metal 600 WF₆ 50 400 10 0.25 purge 600 — — 400 100.5 reduce 600 TEB 40 400 10 0.1 purge 600 — — 400 10 0.8

Radicals provided by plasma generators can facilitate deposition ofmetal-containing layers at the low temperatures of ALD processing.Structures and methods of depositing metals and metal-containing layerswith radical enhancement are provided in patent application having Ser.No. 09/392,371, filed Sep. 8, 1999 and entitled IMPROVED APPARATUS ANDMETHOD FOR GROWTH OF A THIN FILM, the disclosure of which isincorporated by reference hereinabove. Another exemplary ALD metalprocess flow is provided in U.S. Pat. No. 5,916,365 to Sherman, issuedJun. 29, 1999, the disclosure of which is incorporated herein byreference.

Methods of Forming Metal Nitride Barrier Liners

FIG. 4 and Tables II to IV below illustrate exemplary processes forforming metal nitride barrier layers lining the structures of FIGS. 9Ato 9E. For simplicity, like reference numerals are employed to refer tothe phases and steps of the metal nitride examples (FIG. 4) thatcorrespond to the general description of FIG. 3.

With reference now to FIG. 4, a gas flow sequence is represented inaccordance with a particular embodiment. In the illustrated example, aconductive nitride, and more particularly a metal nitride, is formed bysupplying the workpiece with a metal source gas alternately with anitrogen source gas. The first or metal phase 107 of each cyclechemisorbs a layer of metal-containing material, desirably in theabsence of the nitrogen source gas. The second or nitrogen phase 111 ofeach cycle reacts or adsorbs a nitrogen-containing material on thedeposited metal-containing layer, desirably in the absence of the metalsource gas. It will be understood that, in other arrangements, the orderof the phases can be reversed, and that the reactant removal or purgesteps can be considered part of the preceding or subsequent reactantpulse.

Surfaces of the damascene structure upon which the lining material is tobe formed are initially terminated to provide a surface that is reactivewith the metal source gas. In the embodiment of FIG. 9A, the exposedsurfaces upon which deposition is desired include sidewalls of theinsulating layers 50, 56 (TEOS in the illustrated embodiment), exposedetch stop layers 54, 58 and the floor of the contact via 62 defined bythe lower conductive element 52 (copper in the illustrated embodiment).These surfaces are preferably prepared for barrier layer formation bydeposition of an adhesion layer, desirably by ALD metal deposition, asdiscussed above, and a further treatment of the metal adhesion layerwith NH₃, for example. Without an adhesion layer, reactants of the metalphase 107 can chemisorb upon the oxide and nitride surfaces of thepreferred damascene structure without separate surface termination.Depending upon the chemistry of the metal phase 107, a surface treatmentof the exposed metal runner 52 can be provided (e.g., with NH₃).

Most preferably, the metal phase 107 is self-limiting, such that no morethan about one atomic monolayer is deposited during the first phase.Desirably, a volatile metal source gas is provided in a pulse 104.Exemplary metal source gases include titanium tetrachloride (TiCl₄),tungsten hexafluoride (WF₆), tantalum pentachloride (TaCl₅), tantalumpentaethoxide, tetrakis(dimethylamino)titanium,pentakis(dimethylamino)tantalum, copper chloride (CuCl) and copperhexafluoroacetylacetonate vinyltrimethylsilane (Cu(HFAC)VTMS).

After a sufficient time for the metal source gas to diffuse into thebottom of the dual damascene contact via, shutting off the flow of themetal source gas ends the metal pulse 104. Preferably, carrier gascontinues to flow in a purge step 106 until the metal source gas ispurged from the chamber.

During the pulse 104, the metal source gas reacts with exposed andterminated surfaces of the workpiece to deposit or chemisorb a“monolayer” of metal-containing species. While theoretically thereactants will chemisorb at each available site on the exposed layer ofthe workpiece, physical size of the adsorbed species (particularly withterminating ligands) will generally limit coverage with each cycle to afraction of a monolayer. In the example of Table II, the ALD processgrows metal nitride layers at roughly 0.35 Å/cycle, such that a fullmonolayer effectively forms from material deposited approximately every15 cycles for TiN, which has a bulk lattice parameter of about 4.2 Å.Each cycle is represented by a pair of metal source gas and nitrogensource gas pulses. “Monolayer,” as used herein, therefore refers to afraction of a monolayer during deposition, referring primarily to theself-limiting effect of the pulse 104.

In particular, the metal-containing species deposited/adsorbed upon theworkpiece is self-terminating such that the surface will not furtherreact with the metal source gas. In the examples set forth below, TiCl₄(Table II) leaves a monolayer of chloride-terminated titanium. WF₆(Tables III and IV) leaves a monolayer of fluorine-terminated tungsten.Similarly, other volatile metal halides will leave halide-terminatedsurfaces, and metal organics, such as tantalum pentaethoxide,tetrakis(dimethylamino)titanium, and pentakis(dimethylamino)tantalum,will leave surface terminated with organic ligands. Such surfaces do notfurther react with the metal source or other constituents of thereactant flow during the metal source gas pulse 104. Because excessexposure to the reactants does not result in excess deposition, thechemistry during the metal phase 107 of the process is said to beself-limiting. Despite longer exposure to a greater concentration ofreactants, deposition on upper surfaces of the workpiece does not exceeddeposition on the via floor.

In a second phase 111 of the cycle 115, a pulse 108 of a nitrogen sourcegas is then provided to the workpiece. In the illustrated examples, thenitrogen source gas comprises ammonia. Preferably, the second phase 111is maintained for sufficient time to fully expose the monolayer ofmetal-containing species left by the first phase 107 to the nitrogensource gas. After a sufficient time for the nitrogen source gas todiffuse into the bottom of the dual damascene contact via, shutting offthe flow of the metal source gas ends the nitrogen pulse 108.Preferably, carrier gas continues to flow in a purge step 110 until thenitrogen source gas is purged from the chamber.

During the nitrogen pulse 108, the nitrogen source gas reacts with orchemisorbs upon the self-terminated metal monolayer left by the firstphase 107. In the embodiments of Tables II and III, this chemisorptioncomprises a saturative ligand-exchange reaction, replacing the halogentermination of the metal monolayer with a nitrogen-containing species.In the embodiment of Table IV, in contrast, an intermediate getter orscavenging phase first removes the halogen termination of the metalmonolayer prior to a nitrogen pulse. In this case, in a third phase thenitrogen-containing species reacts with adsorbs upon the metal leftexposed by the getter phase. In either case, a metal nitride is therebyformed, preferably in a single monolayer. Desirably, the process leavesa stoichiometric metal nitride. As discussed with respect to the metalphase 107, the monolayer need not occupy all available sites, due thephysical size of the adsorbed species. However, the second phase 111also has a self-limiting effect.

In particular, the nitrogen source gas reacts with the metal-containingspecies chemisorbed onto the workpiece surface during the previous pulseof metal source gas. The reaction is also surface terminated, sinceammonia during the pulse 108 will not react with nitrogen and NH_(x)tails terminating the metal nitride monolayer. Moreover, temperature andpressure conditions are arranged to avoid diffusion of ammonia throughthe metal monolayer to underlying materials. Despite longer exposure toa greater concentration of reactants in this saturative, self-limitingreaction phase 111, the thickness of the metal nitride formed on uppersurfaces of the workpiece does not exceed the thickness of the metalnitride formed on the via floor.

The metal phase 107 (including metal source pulse 104 and purge 106) andnitrogen phase 108 (including nitrogen source pulse 108 and purge 110)together define a cycle 115 that is repeated in an ALD process. Afterthe initial cycle 115, a second cycle 115 a is conducted, wherein ametal source gas pulse 104 a is again supplied. The metal source gaschemisorbs a metal-containing species on the surface of the metalnitride formed in the previous cycle 115. The metal-containing speciesreadily react with the exposed surface, depositing another monolayer orfraction of a monolayer of metal-containing species and again leaving aself-terminated surface that does not further react with the metalsource gas. Metal source gas flow 104 a is stopped and purged 106 a fromthe chamber, and (according to Tables II and III) a second phase 111 aof the second cycle 115 a provides nitrogen source gas to nitridize thesecond metal monolayer. According to the example of Table IV, thenitrogen phase is preceded by an intermediate getter or scavengingphase.

The cycle 115 a is repeated at least about 10 times, and more preferablyat least about 20 times, until a sufficiently thick metal nitride isformed to serve a barrier function in the dual damascene structure.Advantageously, layers having a thickness of less than about 200 Å, andmore preferably less than about 100 Å, can be formed with near perfectstep coverage by the methods of the preferred embodiments.

EXAMPLES

The tables below provide exemplary process recipes for forming metalnitride layers suitable for barrier applications in dual damascenemetallization schemes for ultra large scale integrated processing. Eachof the process recipes represents one cycle in a single-wafer processmodule. In particular, the illustrated parameters were developed for usein the single-wafer ALD module commercially available under the tradename Pulsar 2000™, available commercially from ASM Microchemistry Ltd.of Finland.

Note that the parameters in the tables below (and also in Table I above)are exemplary only. Each process phase is desirably arranged to saturatethe via and trench surfaces. Purge steps are arranged to removereactants between reactive phases from the vias. The examples hereinhave been conducted upon planar, unpatterned wafer surfaces in a Pulsar2000™ reaction chamber, from ASM Microchemistry Ltd. of Finland. SimilarALD processes have been determined to achieve better than 90% stepcoverage in voids with aspect ratios of greater than about 20. In viewof the disclosure herein, the skilled artisan can readily modify,substitute or otherwise alter deposition conditions for differentreaction chambers and for different selected conditions to achievesaturated, self-terminating phases at acceptable deposition rates.

Advantageously, the ALD processes described herein are relativelyinsensitive to pressure and reactant concentration, as long as thereactant supply is sufficient to saturate the trench and via surfaces.Furthermore, the processes can operate at low temperatures Workpiecetemperature is preferably maintained throughout the process betweenabout 300° C. and 500° C. to achieve relatively fast deposition rateswhile conserving thermal budgets during the back-end process. Morepreferably, the temperature is maintained between about 350° C. and 400°C., and most preferably between about 380° C. and 400° C. Pressure inthe chamber can range from the milliTorr range to super-atmospheric, butis preferably maintained between about 1 Torr and 500 Torr, morepreferably between about 10 Torr and 100 Torr. TABLE II Carrier ReactantFlow Flow Temperature Pressure Time Phase (slm) Reactant (sccm) (° C.)(Torr) (sec) metal 400 TiCl₄  20 400 10 .05 purge 400 — — 400 10 0.8nitrogen 400 NH₃ 100 400 10 0.75 purge 400 — — 400 10 1.0

Table II above presents parameters for ALD of a titanium nitride (TiN)barrier into trenches and contact vias of a dual damascene structure. Asnoted, the metal source gas comprises titanium tetrachloride (TiCl₄),the carrier gas comprises nitrogen (N₂) and the nitrogen source gaspreferably comprises ammonia (NH₃).

In the first phase of the first cycle, TiCl₄ chemisorbs upon the oxide,nitride, metal and/or OH- or NH_(x)-terminated surfaces of the dualdamascene trenches and contact vias. The metal source gas preferablycomprises a sufficient percentage of the carrier flow, given the otherprocess parameters, to saturate the damascene surfaces. A monolayer oftitanium complex is left upon the trench and via surfaces, and thismonolayer is self-terminated with chloride.

Desirably, the reactor includes a catalyst to convert the metal sourcegas to a smaller and/or more reactive species. In the illustratedembodiment, the preferred reaction chamber comprises titanium walls,which advantageously convert TiCl₄ to TiCl₃ ⁺. The smaller speciesreadily diffuse into vias, occupy more reactive sites per cycle and morereadily chemisorb onto the active sites. Accordingly, the catalystenables faster deposition rates. The skilled artisan will readilyappreciate that other catalysts can be employed for other chemistries.

After the TiCl₄ flow is stopped and purged by continued flow of carriergas, a pulse of NH₃ is supplied to the workpiece. Ammonia preferablycomprises a sufficient percentage of the carrier flow, given the otherprocess parameters, to saturate the surface of the metal-containingmonolayer. The NH₃ readily reacts with the chloride-terminated surfaceof the metal monolayer in a ligand-exchange reaction, forming amonolayer of titanium nitride (TiN). The reaction is limited by thenumber of available metal chloride complexes previously chemisorbed.Neither ammonia nor the carrier gas further reacts with the resultingtitanium nitride monolayer, and the monolayer is left with a nitrogenand NH_(x) bridge termination. The preferred temperature and pressureparameters, moreover, inhibit diffusion of ammonia through the metalmonolayer.

In the next cycle, the first phase introduces TiCl₄, which readilyreacts with the surface of the titanium nitride monolayer, again leavinga chloride-terminated titanium layer. The second phase of the secondcycle is then as described with respect to the first cycle. These cyclesare repeated until the desired thickness of titanium nitride is formed.

In the illustrated embodiment, carrier gas continues to flow at aconstant rate during both phases of each cycle. It will be understood,however, that reactants can be removed by evacuation of the chamberbetween alternating gas pulses. In one arrangement, the preferredreactor incorporates hardware and software to maintain a constantpressure during the pulsed deposition. The disclosures of U.S. Pat. No.4,747,367, issued May 31, 1988 to Posa and U.S. Pat. No. 4,761,269,issued Aug. 2, 1988 to Conger et al., are incorporated herein byreference. TABLE III Carrier Reactant Flow Flow Temperature PressureTime Phase (slm) Reactant (sccm) (° C.) (Torr) (sec) metal 600 WF₆  50400 10 0.25 purge 600 — — 400 10 0.25 nitrogen 600 NH₃ 100 400 10 0.5purge 600 — — 400 10 1.0

Table III above presents parameters for ALD of tungsten nitride (WN). Asnoted, the metal source comprises tungsten hexafluoride (WF₆), thecarrier gas comprises nitrogen (N₂) and the nitrogen source gaspreferably comprises ammonia (NH₃). During each of the reaction phases,the reactants are supplied in sufficient quantity for the given otherparameters to saturate the surface.

In this case, the metal monolayer formed in the metal phase isself-terminated with fluoride, which does not readily react with WF₆under the preferred conditions. The preferred nitrogen source gas,however, reacts with or adsorbs upon the fluoride-terminated surfaceduring the nitrogen phase in a reaction limited by the limited supply oftungsten fluoride complexes previously adsorbed. Moreover, nitridationleaves a nitrogen and NH_(x) termination that does not further reactwith excess ammonia in the saturative phase. TABLE IV Carrier ReactantFlow Flow Temperature Pressure Time Phase (slm) Reactant (sccm) (° C.)(Torr) (sec) metal 400 WF₆ 50 400 10 0.25 purge 400 — — 400 10 0.8reduce 400 TEB  50 400 10 0.01 purge 400 — 400 10 0.5 nitrogen 400 NH₃100 400 10 0.25 purge 400 — — 400 10 0.5

Table IV above presents parameters for another ALD process for formingtungsten nitride (WN). The illustrated embodiment is particularlyadvantageous for directly depositing a barrier layer upon metal at thevia floor and insulating surfaces of the trench and via, without anintermediate adhesion layer. As noted, the metal source comprisestungsten hexafluoride (WF₆), the carrier gas comprises nitrogen (N₂) andthe nitrogen source gas preferably comprises ammonia (NH₃). In thiscase, a getter or scavenger removes the ligands left by the metal phase.In particular, a strong reducer, comprising TEB (triethyl boron) in theillustrated embodiment, reduces or otherwise removes thehalogen-terminated metal complex monolayer. The nitrogen source gas thenreadily reacts with the reduced metal surface. In other arrangements,the getter can replace the halogen-termination in a ligand-exchangereaction, desirably leaving a surface reactive with a subsequentnitrogen-containing species. The nitrogen phase saturates the reactionsites left by the getter phase (i.e., the exposed tungsten surface inthe illustrated embodiment) and leaves a nitrogen and NH_(x) terminationthat does not further react with excess ammonia in the saturative phase.

The intermediate reduction phase results in a metal nitridecrystallinity that exhibits lower resistivity than films formed by theligand-exchange reaction of Table III. Such lowered resistivity isadvantageous for the preferred dual damascene barrier context, where thebarrier is placed in the conductive path of integrated circuit wires.

Moreover, the intermediate scavenger, as represented by the TEB pulse ofTable IV, binds and carries away the halide tails left by the previousmetal phase prior to introduction of the ammonia phase. Advantageously,the ammonia phase reacts directly with metal formed in the first phase,rather than liberating hydrogen halides (e.g., HF) in a ligand-exchangereaction. In contrast to HF, the complex produced by binding halides tothe getter or scavenger does not corrode sensitive surfaces such as themetal at the bottom of the damascene structure. Accordingly, the metalline 52 of the dual damascene structure is protected from corrosiveeffects of HF or other halide species. The process of Table IV has beenfound particularly advantageous where, as in the preferred embodiment,the metal line 52 comprises copper. Etching of the copper is minimizedand uniformity of the blanket metal nitride deposition is therebyimproved.

Once an initial, thin layer (e.g., about 3-10 nm) of metal nitride(e.g., WN) is formed by the method of Table IV, further deposition ofbarrier and/or adhesion materials can proceed without the intermediatescavenger phase. Two phase cycles employing ligand-exchange reactionscan more efficiently produce a thicker barrier layer over the initiallayer. For example, WN by the method of Table IV can be followed byfurther deposition of TiN, such as by the method of Table II. The upperTiN surface of a WN/TiN barrier demonstrates better compatibility withsome process flows.

Methods of Forming Metal Seed Layers

After formation of the metal nitride barrier layer, a seed layer may bedesirable, depending upon the method to be employed for filling the dualdamascene structure and the conductivity of the deposited barrier layer.In the illustrated embodiment, a copper filler is desirablyelectroplated over the illustrated metal nitride barriers. Accordingly,a highly conductive seed layer is preferably first formed over thebarrier layer.

As is known in the art, the seed layer preferably comprises a metallayer, more preferably copper, and can be deposited by any of a numberof processes. For example, state-of-the-art processing employs PVD orsputtering to form a copper seed layer. In conjunction with high stepcoverage obtained in forming the prior metal nitride barrier layer byALD, such methods may be adequate for many dual damascene schemes.

Preferably, a CVD process is employed to deposit the seed layer withhigher step coverage. Metal organic CVD (MOCVD) techniques aredisclosed, for example, by Wolf et al., “Process and equipmentsimulation of copper chemical vapor deposition using Cu(HFAC)VTMS,”Microelectronic Engineering, Vol. 45, No. 1, pp. 15-27 (February 1999),the disclosure of which is incorporated herein by reference.

Most preferably, the seed layer is also formed by ALD. The volume savedby high step coverage formation of one or more of the adhesion, barrierand seed layers thus contributes to a higher-conductivity line due to agreater volume available for the more conductive filler metal andincreased chance of completely filling the contact vias and trenches.TABLE V Carrier Reactant Flow Flow Temperature Pressure Time Phase (slm)Reactant (sccm) (° C.) Torr) (sec) metal 400 CuCl  4 350 10 0.2 purge400 — — 350 10 0.5 reduce 400 TEB 40 350 10 0.2 purge 400 — — 350 10 0.5

Table V above illustrates an ALD pure metal process, similar to that ofTable I above. In alternating phases, copper chloride is first adsorbedand then reduced by TEB. Advantageously, copper chloride is a smallerreactive species compared to organic copper species, facilitating rapidand more complete saturation of reactive sites on the workpiece.

Resultant Trench and Via Liners

Referring now to FIG. 10, the dual damascene structure of FIG. 9A isillustrated with a high step coverage lining layer 150, constructed inaccordance with processes set forth above. As previously noted,depending upon the materials of the via and trench structure and thechemistries of the various deposition steps, the liner 150 can comprisean initial metal adhesion layer in addition to a metal nitride barrierlayer. The lining layer 150 can comprise, for example, a bilayer ofW/TiN, W/WN, Ti/TiN, Ti/WN, and any of a number of other combinations ofadhesion film and barrier film. In the example of Table IV, the barrierlayer is deposited directly over metal and insulating surfaces of thedual damascene structure, and can optionally comprise a WN/TiN bilayer.Preferably, at least one of the sublayers is formed by ALD, inaccordance with the methods disclosed above.

In accordance with the barrier needs of dual damascene processing, andparticularly in conjunction with fast-diffusing copper metal filler, themetal nitride barrier layer of the lining layer 150 is formed to aboutthe minimal thickness necessary for adequate performance of its barrierfunction. Accordingly, the metal nitride layer lining the deep trenchand via structure preferably has a thickness greater than about 20 Å. Atthe same time, high step coverage provided by the methods disclosedherein enable formation of the desired thickness uniformly over allsurfaces of the trench 60 and contact via 62, including insulatingsidewalls and a conductive via floor. Accordingly, the metal nitrideliner within the via 62 is preferably no more than about 200 Å at anypoint of the structure and at any point during the process. Morepreferably, the metal nitrides of the preferred embodiments aredeposited to a thickness of between about 20 Å and 100 Å, and mostpreferably between about 40 Å and 80 Å.

Under the preferred conditions, material sufficient for a fraction of amonolayer is deposited per cycle, due to the physical size of thechemisorbed species preventing occupation of all available sites,particularly if the adsorbed species include organic ligands. In exampleof Table II, TiN grows at about 0.35 Å/cycle, such that preferablygreater than about 50 cycles, more preferably between about 60 and 300cycles, and most preferably between about 60 and 200 cycles areperformed to produce an adequate TiN barrier layer to prevent copperdiffusion.

As noted, the methods described herein enable extremely high stepcoverage (defined as a thickness of the liner on the bottom of the viaas a ratio of the thickness of the liner on sidewalls of the via), evenof the high aspect ratio trench and via structures of the preferredembodiments. The lining layer 150, and particularly ALD-formed film(s)within the liner 150, preferably exhibit step coverage greater thanabout 90%, more preferably greater than about 93%, and most preferablygreater than about 97%.

With reference now to FIG. 11, a seed layer 155 is optionally formedover the lining layer 150. As noted above, such a seed layer 155 isdesirable where the filling metal is to be deposited by electroplatingand where the lining layer 155 demonstrates inadequate conductivity foreffective electroplating. Under such conditions, the seed layer 155 canbe deposited by PVD, more preferably by CVD and most preferably by ALD.In the illustrated embodiment, a “pure” copper is employed for the seedlayer. In other arrangements, tungsten can be used as an electroplatingseed layer. In still other arrangements, no seed layer is employed overthe lining layer 150, such as in process flows preceding anon-electroplating fill procedure or where the barrier layer isadequately conductive (e.g., tungsten nitride), and enables directnucleation of electroplated copper.

Referring now to FIG. 12, the lined damascene structure is then filledwith a highly conductive metal 160. In the illustrated embodiment, wherea seeding film is formed over the lining layer 150, the filler metal 160preferably comprises electroplated copper. In other arrangements, metalsuch as aluminum can be deposited under high pressure and/or hightemperatures to aid reflow into the deep trench and via structures, aswill be appreciated by the skilled artisan. Effective barriers are alsoimportant in preventing spiking during the harsh conditions attendingsuch deposition processes.

With reference now to FIG. 13, the structures are then planarized bychemical mechanical planarization (CMP) or other etch back process toleave isolated lines 170 within the trenches 60, having integralcontacts 180 extending downwardly therefrom. Diffusion of the fillermetal 160 is prevented both during the fill process as well as duringany high temperature processing that follows.

Although the foregoing invention has been described in terms of certainpreferred embodiments, other embodiments will be apparent to those ofordinary skill in the art. For example, while processes are specificallyprovided particular lining materials, the skilled artisan will readilyappreciate that ALD methods can be applied to lining damascenestructures with other materials. Moreover, although illustrated inconnection with a particular process flow and structure for dualdamascene metallization, the skilled artisan will appreciate variationsof such schemes for which the methods disclosed herein will haveutility. Additionally, other combinations, omissions, substitutions andmodification will be apparent to the skilled artisan, in view of thedisclosure herein. Accordingly, the present invention is not intended tobe limited by the recitation of the preferred embodiments, but isinstead to be defined by reference to the appended claims.

1-26. (canceled)
 27. A metallization process, comprising: forming anopening in a porous low k dielectric material above a semiconductorsubstrate in a process chamber to expose at least part of an underlyingconductive element; depositing no more than about one monolayer of atantalum-containing species on surfaces of the opening; reacting the nomore than about one monolayer with a reducer; and forming a lining layerby reacting a reactant species with the no more than about one monolayerafter reacting the no more than about one monolayer with the reducer andbefore introducing any other reactants into the reaction chamber. 28.The method of claim 27, wherein the reactant species is a non-radicalspecies.
 29. The process of claim 28, wherein the reactant species is anitrogen precursor.
 30. The process of claim 29, wherein the reactantspecies is ammonia.
 31. The method of claim 27, wherein depositing theno more than about one monolayer comprises: introducing a tantalumprecursor into the process chamber; and removing the tantalum precursorfrom the process chamber before reacting the no more than about onemonolayer with the reducer.
 32. The process of claim 27, wherein thetantalum precursor comprises an organic ligand.
 33. The process of claim32, wherein the tantalum precursor is pentakis(dimethylamino)tantalum.34. The process of claim 27, wherein the tantalum precursor comprises ahalide ligand.
 35. The process of claim 34, wherein the tantalumprecursor is TaCl₅.
 36. The process of claim 27, wherein the reducer istriethyl boron.
 37. The process of claim 27, wherein the lining layerhas a step coverage of greater than about 90%.
 38. The process of claim27, wherein the opening has a width of less than about 0.35 μm.
 39. Amethod for semiconductor processing, comprising: providing a porous lowk dielectric material overlying a conductive material on a semiconductorsubstrate in a process chamber, the porous low k dielectric materialhaving an opening exposing at least part of the conductive material;forming a lining layer directly on surfaces of the opening, whereinforming the lining layer comprises: introducing a metallic precursorhaving organic ligands into the process chamber to self-limitinglydeposit a layer of a metal-containing species on the surfaces of theopening; reacting the layer of the metal-containing species with areducer.
 40. The process of claim 39, further comprising reacting asecond precursor with the layer of the metal-containing species afterreacting the layer of the metal-containing species with the reducer andbefore introducing any other precursor into the reaction chamber,wherein the lining layer comprises a metallic compound.
 41. The processof claim 39, further comprising: removing the metallic precursor fromthe reaction chamber after introducing the metallic precursor and beforereacting the layer of the metal-containing species with the reducer; andremoving the reducer from the reaction chamber after reacting the layerof the metal-containing species with the reducer and before introducingany other precursor into the reaction chamber.
 42. The process of claim41, further comprising sequentially repeating introducing a metallicprecursor, removing the metallic precursor, reacting the layer of themetal-containing species with the reducer, and removing the reducer fromthe reaction chamber until the lining layer reaches a desired thickness.43. The process of claim 42, wherein the lining layer comprises puremetal.
 44. The process of claim 42, wherein the lining layer comprises ametal-containing compound.
 45. The process of claim 39, wherein theopening comprises a dual damascene trench and contact structure.
 46. Theprocess of claim 39, wherein the reducer is a non-radical reducer. 47.The process of claim 46, wherein the reducer is triethyl boron.